John Philoponus of Alexandria, a sixth-century philosopher and theologian, is best known for his radical attempts to refute fundamental tenets of contemporary Aristotelian–Neoplatonic school philosophy. His main historical significance lies in the fact that he anticipated by centuries the early modern emancipation of natural philosophy from Aristotelian dogmatism. Philoponus (literally Lover of Work), or John the Grammarian, as he called himself, is commonly labeled a Christian Neoplatonist, but this epithet is misleading. Philoponus was a Christian, most likely by birth, and he received the standard philosophical training available at Alexandria in his day. Thus, his philosophical orientation was not a matter of choice, and his fierce rationalism, which he employed also as a tool to resolve controversial questions that divided Christianity, bears no resemblance to the genuine Christian Neoplatonism of Pseudo-Dionysius, the Areopagite (c. 500). Roughly 100 years after his death, the Third Council of...